This is a continuation of research project NS-09871, entitled Neuropharmacology-Anesthesia and the Nervous System (Pain Control). The research projects proposed herein are extensions of the previous studies but with considerable departure from past approaches, and are aimed at the study of activity of sensory neurons in the central nervous system, modulated by anesthetics and analgesics while physiological parameters are strictly maintained within the normal range. It is proposed to study the pharmacologic effects of anesthesia, utilizing microelectrode recording techniques with the aid of a computerized statistical data analysis program available in our laboratory, at the dorsal horn of spinal cord and the nucleus reticularis gigantocellularis of the pontomedullary reticular formation areas known to transmit nociceptive information. The study is aimed at the comparison of the data in these areas to clarify the major sites and modes of action of the production of analgesia by the agents studied, to investigate the interaction among the nuclear groups and to test our hypothesis that anesthetics have a preferential depressant effect upon the "central nociceptors" while leaving the activity of other neurons relatively unaffected. To simulate surgical stimuli, a thermal stimulus will be used, which is controllable, reproducible, conveniently applied and causes minimal tissue damage.